Adjustable ring-core magnetometer with high sensitivity



Jan. 7, 1969 w, A, ER 3,421,074

ADJUSTABLE RING-CORE MAGNETOMETER WITH HIGH SENSITIVITY Filed July 29. 1965 Sheet of 2 Fig. 2

N as Fig.4

OSCILLATOR AMPLIFIER .53

INVENTOR WILL/AM A. GEYGER DECEASED BY ELLA 657651? N e'xscum/x ATTORNEY Jan. 7, 1969 w. A. GEY GER 3,421,074

ADJUSTABLE RING-CORE MAGNETOMETER WITH HIGH SENSITIVITY Filed July 29, 1965 Sheet 2. of 2 SECOND-HARMONIC DETECTOR WINDING I05 RING-CORE m3 A-o EXCITATION 'RoTARY RING /23 WINDING /0/ -cIRcuI AR CENTER PIECE /2/ FIRST fP SECOND BAN o PASS BAN 0- PASS FILTER FILTER EXGITATION Q I- POLARITY OSCILLATOR SENSITIVE AMPL. D-C P INSTRUMENT FREQUENCY P I,

DOUBLER E I //0 2f I M PHASE- SENSITI VJ RECTIFIER [/5 VENTOR WILL/AM A. GEYGER DECEASED 5r ELLA GEYGER sxscurmx ATTORNEY United States Patent 3,421,074 ADJUSTABLE RING-CORE MAGNETOMETER WITH HIGH SENSITIVITY William A. Geyger, deceased, late of Takoma Park, Md., by Ella Geyger, executrix, Takoma Park, Md., assignor to the United States of America as represented by the Secretary or the Navy Filed July 29, 1965, Ser. No. 477,085 US. Cl. 32443 Int. Cl. G01r 33/02 Claims ABSTRACT OF THE DISCLOSURE A ring core magnetometer which uses a toroidal core in combination with a primary A.C. winding mounted thereon. The combination is made rotatable with respect to a diametrically disposed secondary winding in order to provide a minimized residual output voltage. Alternatively, two ring shape cores with serially connected A.C. windings mounted thereon are made rotatably adjustable within a common diametrically disposed secondary windmg.

the design of magnetometers to reduce the output voltage to a minimum when the magnetic field surrounding the core is zero. The reduction of the zero field output voltage also relaxes the filter requirements of the energizing source and also minimizes the effects of second harmonics from the energizing source. In the past such reduction of the zero field output voltage was attempted by closely matching the magnetic characteristics of the two core elements of the magnetometer.

In a first embodiment of this invention a toroidal core together with an AC. winding thereon is made rotatable within a diametrically disposed secondary winding. In a second embodiment of this invention, two ring shaped cores with serially connected A.C. windings thereon are rotatably adjustable within a common diametrically disposed secondary winding.

It is an object of this invention to provide an improved magnetometer in which the zero field output voltage is reduced to a minimum.

It is another object of this invention to provide an improved ring core type magnetometer in which a toroidal core and an exciting winding wound thereon are rotatable precisely within a diametrically disposed second harmonic winding of said magnetometer.

It is a further object of this invention to provide two ring cores with energizing windings thereon serially connected and rotatable within a diametrically disposed secondary winding.

It is yet a further object of this invention to provide an improved magnetometer in which the filter circuit requirements are minimized.

It is still another object of this invention to provide an improved magnetometer in which the second harmonic feed through effects of the excitation voltage source are reduced to a minimum.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same 3,421,074 Patented Jan. 7, 1969 ICC becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIG. 1 illustrates a magnetometer circuit in which a ring core element is rotatable in a second harmonic winding;

FIG. 2 of the drawings illustrates a magnetometer of this invention in which two ring cores are rotatable within a diametrically disposed second harmonic winding;

FIG. 3 of the drawings illustrates wave forms resulting from various angular positions of the cores of FIG. 2 of the drawings;

FIG. 4 is a cross-sectional view of the two-core unit of FIG. 2 of the drawings; and

FIG. 5 illustrates a circuit of a magnetometer in which the ring core and excitation winding are rotatable within a diametrically disposed second harmonic detector wind- 1ng.

Referring now to FIG. 1 of the drawings, a ring core magnetometer 11 is illustrated with an AC. energizing winding 13 wound around core 15. The AC. energizing winding 13 and core 15 are rotatable through an angle a in either direction. The size of the angle a as shown in FIG. 1 does not denote a limitation in .the actual angular displacement but merely the direction of angular displacement of the core and energizing winding with respect to the second harmonic winding 17. The primary or A.C. energizing winding 13 is shown connected to a secondary winding 19 of transformer 21 through a series circuit including capacitor 23, linear inductor 25 and meter 27. An AC. voltage source 29 is shown connected to the primary winding 31 of transformer 21. Second harmonic winding 17 is connected to an output indicating meter 32.

In operation, the magnetometer 11 of FIG. 1 is placed preferably in an environment having azero magnetic field and then the core and winding are rotated within the second harmonic winding 17 until a null is reached in the output indicating meter 32.

Referring now to FIGS. 2, 3 and 4 of the drawings an oscillator 33 is shown connected to a source of AC. voltage at terminals 35 and 37, the output of oscillator 3-3 is fed to the input circuit ofamplifier 39 and the output of amplifier 39 ,is connected to the energizing windings 53 and 57 of cores 51 and 55, respectively, through transformer 41.

A current meter 43 and a volt meter 45 are provided in the primary or energizing circuit of the magnetometer. In FIG. 3 of the drawings a voltage E is the output voltage of second harmonic winding 65 and is comprised of a combination of a voltage E and E which are output voltages which are caused by windings 53 and 57, respectively.

The core 51 and winding 53 are rotated with respect to core 55 and winding 57 until a null or zero voltage output is indicated by meter 67. It can be seen in the diagram of FIG. 3 that E wil be substantially zero as a result of a combination of voltages E and E for any angle 0 once the angular position of core 51 with respect to core 55 has been determined for a minimum zero field output voltage. The second harmonic winding which is diametrically disposed is connected to a meter 67 and to a capacitor 69. It may be noted that terminals 61 and 63 of FIGS. 2 and 4 of the drawings are in actuality connected to two separate core windings. That is, terminal 61 is connected to winding 53 and terminal 63 is connected to winding 57. The serial connection of the two windings is completed by the connection of conductor 71. A coaxial shaft and bearing members mounting each of the cores rotatably on the shaft may be provided for precise adjustments.

Referring now to FIG. 5 of the drawings, in which an adjustable ring core magnetometer circuit is shown comprising an A.C. excitation winding 101 placed upon a core 103 and rotatable through an angle a with respect to a second harmonic detector winding 105. The A.C. excitation winding 101 is energized by an excitation oscillator 107 having a voltage E and a frequency f with a current of flow I through the A.C. excitation winding 101. The voltage E, from the excitation oscillator 107 is fed through a first bandpass filter 109, The output of excitation oscillator 107 is also fed to the input circuit of a frequency doubler 110' with the frequency of the input being f and the output of the frequency doubler being 2f The output of the frequency doubler provides a reference voltage E having the frequency of Zf which is fed to a first pair of terminals of a phase sensitive rectifier 115. The second harmonic detector winding 105 is shown connected to a second bandpass filter 117 designed to pass voltages having the frequency of 2 which are applied to input terminals of A.C. amplifier 119. The output terminals of A.C. amplifier 119 are connected to a second pair of terminals of the phase sensitive rectifier 115. The amplified voltage represents an amplification of the second har monic voltages appearing across the second harmonic detector winding and this voltage applied to the phase sensitive rectifier is designated as E The phase sensitive rectifier may be a ring diode circuit having four rectifiers connected in series to form a ring with terminals therebetween. The output of the phase sensitive rectifier is provided with a polarity sensitive D.C. instrument M which is connected to the phase sensitive rectifier 115 The current flow I is a current flow from the output circuit of the phase sensitive rectifier indicating the strength of the second harmonic voltages appearing in the detector winding 105 when the magnetometer is placed in the magnetic field to be measured. The comparison of the reference signals E and the second harmonic voltage E by the phase sensitive rectifier circuit 115 will provide an output voltage which has a magnitude proportional to the strength of the magnetic field to be measured and will have a polarity depending upon the direction of the magnetic field to be measured.

A shaft or center piece 121 and a rotary ring 123 may be employed to provide for precise rotation of the core. The rotary ring carries the core and rotates around the center piece 121. An index marker may be placed on the rotary ring to show the angular position of the core.

For operation of the basic ring core magnetometer, reference is made to acopending application of William A. Geyger, Ser. No. 143,988, entitled Second Harmonic Flux Gate Magnetometer, filed Oct. 9, 1961, now abandoned or to The Ring Core Magnetometer, A New Type of Second-Harmonic Flux Gate Magnetometer, AIEE Transactions 81, Pt. 1, page 65, March 1962.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A second harmonic ring core magneto-meter comprising:

a toroidal saturable core,

a primary energizing winding on said core,

a secondary winding surrounding said toroidal core with the plane of said winding being perpendicular to the plane of said core,

means for rotating said toroidal core and said primary energizing winding with respect to said secondary winding in the plane of said toroidal core,

means for connecting said energizing winding to a source of A.C. voltage, and

output indicating means connected to said secondary winding.

2. A second harmonic ring core magnetometer comprising:

a toroidal saturable core,

an energizing winding on said core,

a second harmonic detector winding surrounding the diameter of said toroidal core with the plane of said winding being perpendicular to the plane of said core, means for rotating said toroidal core and said energizing winding within said second harmonic detector winding in the plane of said toroidal core,

means provided on said toroidal core whereby said core and energizing winding may be precisely rotated to a desired angular position,

index means for indicating the angular position of said toroidal core and energizing Winding with respect to said second harmonic detector winding, means for connecting said energizing winding to a source of A.C. voltage,

output indicator means connected to said second harmonic detector winding.

3. The second harmonic flux-gate magnetometer comprising:

a first toroidal core,

the first energizing winding wound thereon,

a second toroidal saturable core,

a second energizing winding wound thereon,

a primary circuit comprising the serial connection of said first energizing winding and said second energizing winding,

said first and second toroidal cores being coaxially disposed in close parallel relationship, means for rotating said first core with respect to said second core, whereby said first core may be rotated with respect to said second core to produce a near zero field output voltage,

means for connecting said primary circuit to a source of A.C. voltage,

a second harmonic winding surrounding the diameters of said first and second toroidal cores, the plane of said second harmonic winding being perpendicular to the planes of said first and second toroidal cores, and

indicating means connected to said second harmonic winding.

4. A second harmonic type flux-gate magnetometer comprising a ring shaped toroidal core,

an energizing winding wound on said core,

means connecting said energizing winding to an A.C.

voltage source,

a second harmonic output winding surrounding the diameter of said toroidal core with the plane of said winding being perpendicular to the plane of said core, means for rotating said core within said output winding in the plane of said core whereby said core may be rotated to an angular position in which the zero field output voltage of the magnetometer is reduced to a minimum,

output indicating means connected to said second harmonic output winding.

5. An adjustable ring core flux-gate magnetometer comprising:

a first toroidal saturable core,

a first energizing winding on said first core,

a second toroidal core,

a second energizing winding on said second core,

a primary circuit comprising said first and second energizing windings connected in series,

means for connecting said primary circuit to an A.C.

voltage source,

said first and second cores being disposed in coaxial parallel relationship, means for rotating said first core with respect to said second core, a second harmonic detector winding surrounding the diameter 5 6 of said first and second cores with the plane of said References Cited Winding being perpendicular to the plane of said UNITED STATES PATENTS core, means connecting said second harmonic output wind- 14 12/1947 D eep et a1 340197 2,476,273 7/1949 Beach 340-197 mg to an output indicating means, 5 2 856 581 10/1958 And d shaft means coaxial with said first and second toroidal re ge cores, OTHER REFERENCES first bearing means rotatably mounting Said first tofoi- Aschenbrenner, H. et al.: An Arrangement to Measure dal core on said shaft means, Rapid Magnetic ariations, Yearbook of Wireless Telesecond bearing means rotatably mounting said second 10 graph and Telephone (German Publication), June 1936,

toroidal core on said shaft means whereby said first pp. 177181.

toroidal core may be precisely rotated with respect 4 a to said second core to provide a minimum zero out- RUDOLPH ROLINEC lmay Examiner put voltage. R. J. CORCORAN, Assistant Examiner. 

